Ignition device for internal combustion engine

ABSTRACT

A low DC voltage boosted by an inverter and a rectifier charges a capacitor a charge on which is, in turn, discharged into an ignition coil under control of a thyristor. Upon starting the engine, the DC voltage is applied to an intermediate terminal of a primary transformer winding in the inverter. Diodes are connected in a circuit for gating the thyristor to prevent the circuit from partly short-circuiting the primary winding through the intermediate terminal.

United States Patent Inventor Yasuo Tada Himeji, Japan Appl. No. 799,260Filed Feb. 14, 1969 Patented Feb. 16, 1971 Assignee Mitsubishi DenkiKabushiki Kaisha, Tokyo, Japan Priority Feb. 19, 1968 Japan 43/ l 2053IGNITION DEVICE FOR INTERNAL COMBUSTION ENGINE 4 Claims, 1 Drawing Fig.

11.8. CI 123/148 Int. Cl. F02p 3/06 Field of Search 123/148 (E), 179(B); 315/209, 209 (CD), 214

[56] References Cited UNITED STATES PATENTS 3,131,327 4/1964 Quinn315/214X 3,251,351 5/1966 Bowers... 123/148 3,352,295 11/1967 Miki123/179B 3,448,732 6/1969 Weiss 123/148E Primary Examiner- Laurence M.Goodridge Attorneys-Robert E. Burns and Emmanuel J. Lobato ABSTRACT: Alow DC voltage boosted by an inverter and a rectifier charges acapacitor a charge on which is, in turn, discharged into an ignitioncoil under control of a thyristor. Upon starting the engine, the DCvoltage is applied to an intermediate terminal of a primary transformerwinding in the inverter. Diodes are connected in a circuit for gatingthe thyristor to prevent the circuit from partly short-circuiting theprimary winding through the intermediate terminal.

PATENIED FEB 1 6 I97! HHHHHHHI IGNITION DEVICE FOR INTERNAL COMBUSTIONENGINE BACKGROUND or THE INVENTION This invention relates to'an ignitiondevice" for use with an internal combustion engine equippedon a notorvehicle or the like and more particularly to improvements in such a.device of capacitor discharge type.

The capacitor discharge type of ignition devices for use with internalcombustion engines comprises generally a source of direct current, aninverter forcohverting a power of direct current provided by the sourceto a power of alternating current and increasing the voltage of theconverted power, a rectifier for rectifying the power of alternatingcurrent from the inverter to provide a power of direct current, acapacitor charged with the power of direct current fromthe rectifier anda switch connected in a discharge circuit for the capacitor andoperative in itsclosed position to discharge the charge on the capacitorinto the associatedignition 'coil to produce an ignition voltage acrossthe latter.

It has been commonly practiced that a source of electrical power for theignitiondevice referred to, that is, the source of direct current asabove described is additionally used as a source of electricalpower foran electric device for starting an internal combustion engine whichignited by the ignition device. In most of motor vehiclesfthe source ofdirect current electric arc across the contacts is scarcely called inquestion while insuring a long useful life of the resulting ignitiondevice.

What is now called in question in the relationship between a circuitconfiguration for compensating for a decrease in direct current voltageapplied to the associated inverter upon starting the engine and acircuit for gating the thyristor. According to Miki patent as abovecited, an, inverter includes a trans former provided on its input orprimary winding with an intermediate terminal separated from its end.tenninals to present a higher turn ratio associated with theintermediate terminal to the output winding of the transformer. Then theprimary winding have selectively supplied thereto an electrical energyis composed of a storage batteryhaving a rating voltage of either 12 or24 volts and the starting electric device is a starting electric motorthrough which a .high load current is required to flow in operation.This flow of high load current through the motor causes a great decreasein voltage across the'sourceof direct current.-For'example, with astorage battery having a rating voltage of 12 volts, the voltagethereacross will range from approximately 8 to 12 volts prior tostarting the associated engine or after ithas been started and it may Idecrease down to a minimum possible magnitude of approxi mately 67percentof the rating voltage particularly when an electric deviceforstarting theassociated engine has a very high currentflowingtherethrough as injstarting the engine in a cold districtQAlthough thevoltagelacross the source for the ignition device is ideally maintainedalways constant this leads to the necessity of providing separatesources of electrical power for the ignition and starting devices.However this measure is difficult to be realizedinvi'ew-of thestandpoint of economy. Therefore it is highly desirable to provide anignition device including means; for compensating for any decrease involtage applied thereto, upon starting the associated engine whereby theengine is. ignited with a sufficient ignition energy even undervoltage'decrease state.

An ignition device for an internal combustion engine rneeting suchrequirements is described'and claimed in U.S. Pat. No. 3,352,295 issuedNov. 14,1967 to Takas Miki and as signed to the same assignee as thepresent application. Like the present invention the cited patentdiscloses in FIGS. 1 and 2 ignition devices for internalcombustionengines including a capacitor. The capacitor has its dischargecircuit adapted to be open. and closed directly by a set of mechanicalcontacts.

; The contacts have then directly applied thereacross a high through theintermediate terminal upon starting the engine and through one of theend terminals'after the engine has been started.

On the other hand, the circuit for gating the thyristor is required tohave an electrical energy supplied by the as sociated source of directcurrent during and after the operation of starting the engine whilesuch: supply of the electrical energy to the gating circuit must beterminated during the suspension of operation of the engine for thepurpose of preventing the source from wastefullyconsuming the electricalenergy. To this end, one conductor can be connected to the source ofdirect current through a switch adapted to be closed upon starting theengine thereby to supply an electrical energy to. the input winding ofthe said transformer through the intermediate terminal while the otherconductor can be connected to the source through another switch adaptedto be closed after the completion of the operation of starting theengine thereby to supply an electrical energy to the input transformerwinding through the one'end terminal with both the conductors connectedto aterminal on the source side of the gating circuit. In this case itis to be noted that means for connecting both the conductors to the saidterminal of the gating circuit be prevented from short-circuiting thatportion disposed between the intermediate and end terminal of the inputtransformer winding. This is because if such short-circuiting occursthen the magnetic core of the transformer is impeded from changing inmagnetic flux resulting in a zero output from the transformer andtherefore from the inverter.

SUMMARY-0F THE-INVENTION Accordingly it is an object of the invention toprovide a new and improved ignition device for use with an internalcombustion engine having a long useful life and including means forcompensating-for a decrease in voltage applied to the device uponstarting the engine and free from any short-circuiting fault whileensuring that'the engine is ignited during the operation thereof withoutany waste of electrical energy during the suspension of operation of theengine.

With this object in view, the invention resides in an ignition device ofcapacitor discharge type for use with an internal combustion engineincluding an ignition capacitor charged with a rectified output from aninverter, and a thyristor connected in a circuit for discharging thecapacitor and a pair of conductors for supplying electrical energies ofdirect current i to an intermediate terminal and an end terminal of aninput transformer winding in the inverter respectively, and a pair ofthe thyristor, the diodes being so poled that a voltage of eitherdispose a thyristor in the discharge circuit for the capacitor.

Because of no electric arc appearing'in thyristors the use of athyristor sufficiently high in dielectric'strength makes itpossipolarity is prevented from causinga short-circuiting current toflow through that portion disposed between the intermediate v and endterminals of the primary transformer winding.

ble to form an ignition device longer in useful life than the mechanicalcontacts as above described. If a set of mechanical contacts such asabove described is connected in a circuit for gating the particularthyristor, the contacts have only applied thereacross a voltagedecreased by a-factor of several. tens as compared with the voltagedirectly provided by .the capacitor as above describedwith the resultthat the occurrence of an BRIEF DESCRIPTION OF THE DRAWING DESCRIPTIONOF THE PREFERRED EMBODIMENT Referring now to the drawing, it is seenthat an arrangement disclosed herein comprises a source of directcurrent 10 such as a 12 v. storage battery equipped on a motor vehicleand an inverter generally designated by the reference numeral 12. Theinverter 12 comprises transformer generally designated by the referencenumeral 14 including a pair of primary or input windings l6 and 18connected in series circuit relationship, a single secondary or outputwinding 20 and a pair of tertiary windings 22 and 24 with all thewindings inductively disposed on a saturable magnetic core 26. Theprimary winding 16 includes a pair of end terminals a and b and anintermediate terminal d while the primary winding 18 includes one endterminal and the other end terminal b common to the primary winding 16.The conventional dot is used to indicate the polarity of each of theprimary and tertiary windings.

A transistor 28 shown as being of the NPN type includes a collectorelectrode connected directly to the end terminal a of the primarywinding 16, a base electrode connected directly to one terminal of thetertiary winding 22 and an emitter electrode connected directly to theground such a vehicles chassis (not shown). Another transistor 30 shownas being also of NPN type includes similarly a collector electrodeconnected directly to the end terminal c of the primary winding 18, abase electrode connected directly to one terminal of the tertiarywinding 24 and an emitter electrode connected directly to the ground.The emitter electrodes of both the transistors 28 and 30 are connectedto the other terminals of the tertiary windings 22 and 24 throughresistors 32 and 34 respectively. v

Another resistor 36 is connected across the collector and baseelectrodes of the transistor 28 for the purpose of first flowing aforward base current through the transistor 28 upon starting theinverter 12. I

A pair of conductors 38 and 40 are connected at one end to the end andintermediate terminals b and d of the primary winding 16 and at theother ends to a pair of stationary contacts A and B of a transfer switch42 including a movable arm M connected to one terminal, in this case,the positive terminal of the source having the negative terminalconnected to the ground. Thus it will be appreciated that the inverter12 is operative to convert a direct current voltage supplied by thesource 10 to an alternating current voltage and increase the lattervoltage.

While the inverter 12 is shown as including the primary windings, thetertiary windings and the transistors in pairs to form a push-pullconfiguration it is to be understood that the inverter may be notnecessarily of the push-pull type, if desired. In the latter case, theprimary winding 18, the tertiary winding 24 and the transistor 30 areomitted.

The secondary or output winding 20 of the transformer 12 has connectedthereacross a single phase full wave rectifier 44 having a pair ofalternating current input tenninals connected to both ends of thewinding 20. The full wave rectifier 44 has one direct current outputterminal connected to the ground and the other direct current outputterminal connected to the ground through an ignition capacitor 46.

An ignition coil of auto transformer type generally designated by thereference numeral 48 includes a primary winding 50 and a secondarywinding 52 with the junction of both the windings connected to thejunction of the rectifier 44 and the capacitor 46. The secondary winding52 has the other end connected to an ignition plug (not shown) and theprimary winding 50 has the other end connected to a thyristor 54. Thethyristor 54 includes an anode electrode connected to the other end ofthe primary ignition winding 50, a cathode electrode connected to theground and a gate electrode 54. The thyristor 54 along with the primaryignition winding 50 serially connected thereto forms a discharge circuitfor the capacitor 46.

In order to gate the thyristor 54, a gating circuit enclosed with adashed block 56 is operatively associated with the thyristor. The gatingcircuit 56 includes a resistor 58 connecting the gate electrode of thethyristor 54 to ground, a gating capacitor 60 connected to the junctionof that cathode electrode 'and the resistor 58, a resistor 62 connectedto the capacitor 60 and a contact breaker 64 connected between thejunction of the capacitor and resistor 60 and 62 respectively and theground. The contact breaker 64 is arranged to be open and closed by acam rotating in synchronization with the rotation of the associatedengine in the well-known manner. The cam, and engine are well known inthe art and therefore they are not illustrated. The breaker 64 is put inits open position at each ignition time of the engine.

The resistor 62 is connected to an input terminal 56A to the gatingcircuit 56 which is, in turn, connected to the conductors 38 and 40through the respective semiconductor diodes 68 and 70 each poled so asto permit a current to flow from the associated conductor 38 or 40 tothe gating circuit 56 therethrough.

The transfer switch 42 as previously described has its movable arm Madapted to engage the contact B upon starting the engine and to engagethe contact A after the completion of the starting operation and whenthe engine is put in operation. However it is noted that when the engineis out of operation the movable arm M assumes its neutral position asillustrated in the drawing. This is, none of the contacts A and B are incontact with the movable arm M.

In order to start the engine, a starting electric motor is connected tothe source 10 through an on-off switch adapted to be closed when themovable arm M engages the contact B, although the motor and the on-offswitch are not illustrated.

The arrangement thus far described is operated as follows:

The inverter 12 is a Royer circuit well known in the art and itsoperation will be briefly described. Upon applying a DC voltage from thesource 10 to the inverter 12 through either one of the contacts A and Bof the switch 42 as the case may be, the transistor 28 is first fired topermit a base current to flow therethrough. Then the transistor 28 isincreasingly conducting through the feedback action of the tertiarywinding 22 until the magnetic core 26 of the transformer 14 is driven tosaturation. When the saturation of the magnetic core 26 has reached apoint of contraflexure, the primary winding 18 has a low voltage inducedin the reverse direction thereacross whereupon the transistor 30 is nowfired, while the transistor 28 becomes nonconducting. Thereafter theprocess as above described is repeated with the conducting transistor30. In this way the transistors 28 and 30 are alternately conducting toproduce across the secondary or output winding 20 an output of squarewaveform having a pulse recurrence frequency corresponding to thevoltage across the source 10 and increased in magnitude or voltage bythe particular turn ratio between the energized portion of the primarywinding and the secondary winding. The output from the transformer 14and therefore the inverter 12 is rectified by the full wave rectifier 44and charges the ignition capacitor 46.

Each time the thyristor 54 is conducting as will be describedhereinafter, the charge on the capacitor 44 is discharged through thedischarge circuit comprising the primary ignition winding 50 and the nowconducting thyristor 54 whereupon a high voltage is induced across thesecondary ignition winding 52 to ignite the engine in the well-knownmanner.

Under these circumstances, the thyristor 54 is controlled by the gatingcircuit 56. More specifically, with the contact breaker 64 closed; avoltage across the gate and cathode electrodes of the thyristor 54 is ofzero magnitude maintaining it nonconducting. Then if the contact breaker64 is open, a charging current flows from the source 10 into thecapacitor 60 through the switch 42 and the conductor 38 or 40 as thecase may be. This charging current also flows through the resistor 58 toprovide a voltage drop thereacross sufficient to gate the thyristor 54whereupon the charge on the capacitor 44 is discharged as abovedescribed, when discharged the capacitor 46 cooperates with the primaryignition winding 50 to generate an oscillatory voltage at the instantthis oscillatory voltage is reversely applied to the anode and cathodeelectrodes of the thyristor 54 the latter is brought into its open stateready for the succeeding ignition operation.

Then the source is connected to the common terminal b of 10 the primarytransformer windings l6 and 18 through the movable arm and contact M andA respectively of the switch 42 and the conductor 38 while at the sametime, it is connected to the input terminal 56A to the gating circuit 56through the movable arm M and contact A of the switch 42, the conductor38 and the diode 68.

Under these circumstances, an output voltage V, from the secondary oroutput winding of the transformer 14 is expressed by Nab ' former 14through the conductor 40 and also to the input terminal 56A to thegating circuit 56 through the diode 70.

Under these circumstances, an output voltage from the secondarytransformer winding 20 is expressed by N; I I Na-n (2) N. II I ari-"(2') V',, output voltage due to primary winding portion betweenterminals 0 and d;

V output voltage due to primary winding portion between terminals d andc; and V n number of turns between terminals d and b of primary winding16. it is also assumed that the primary windings l6 and 18 are equal inthe number of turns to each other.

From the above equations (2) and (2') it is seen that V,

is higher than V However it will be appreciated that the number of turnsn between the terminalsd and b of the primary winding 16 can be selectedso as to render both the output voltages V, and V", approximately equalto each other in order to compensate for a difference between outputvoltages in the normal and starting operations of the engine.

In order to discuss the effect of the diodes 68 and 70, it is nowassumed that the conductors 38 and 40 have been connected directly tothe input terminal 56A to the gating circuit 56 with the diodes 68 and70 omitted. Under the assumed conditions, that portion disposed betweenthe terminals b and d of 5 the primary transformer winding 16 isshort-circuited by the conductors 38 and 40. Thus in the operation ofthe inverter 12, a short-circuiting current flows through that portiondisposed between the terminals b and d of the primary winding 16resulting in a decrease in output voltage from the secondary winding 20of the transformer 14. The purpose of the diodes 68 and 70 is to preventthis flow of short-circuiting current.

lclaim:

1. An ignition device for use with an internal combustion engine,comprising, in combination:

1. a source of direct current;

2. inverter means including a transformer comprising a saturablemagnetic core, an input winding, an output winding and a feedbackwinding, all said windings being inductively disposed around saidmagnetic core and a transistor connected to both said input winding andsaid feedback winding;

3. said primary winding having an end terminal and an intermediateterminal presenting to said output winding a turn ratio higher than doessaid end terminal;

4. a first conductor connected to said end terminal of said primarytransformer winding and capable of being energized by said source;

. a second conductor connected to said intermediate terminal of saidprimary transformer winding and capable of being energized by saidsource;

6. a transfer switch connected between said source and said first andsecond conductors such that, the same connects said source to saidsecond conductor upon starting the engine and to said first conductorafter the engine has been started and when it is in operation;

7. a rectifier for rectifying the output of the output winding of saidtransformer and an ignition capacitor charged with the rectified outputof the output winding of said transfonner of said inverter means;

. an ignition coil including a primary winding and a secondary windinginductively coupled to each other, said pri mary winding having one endconnected to said ignition capacitor;

9. a thyristor for controlling said ignition capacitor and operative inits closed state to permit said ignition capacitor to be discharged intosaid primary ignition coil winding to produce an ignition voltage acrosssaid secondary coil ignition winding, said thyristor having a controlterminal;

.40 10. a gating circuit controlling said thyristor and having an inputterminal, means operable in synchronism with the rotation of the engineto produce a gating signal and an output terminal connected with thecontrol terminal of said thyristor; and

l l. a pair of semiconductor diodes having input and output tenninals,means connecting the output terminals of both of said diodes to theinput terminal of said gating circuit, means connecting the inputtenninal of one of said diodes with said first conductor, and meansconnecting the input terminal of the other of said diodes with saidsecond conductor.

2. An ignition device as claimed in claim 1, wherein said transfonner ofsaid inverter means: includes additionally another of said invertermeans includes additionally another input winding and a separatefeedback winding inductively disposed around said magnetic core, andwherein another transistor is connected to both said another inputwinding and said separate feedback winding, said transistors beingalternately turned on and off.

3. An ignition device as claimed in claim 1, wherein said primaryignition winding is serially connected to said thyristor, the seriesarrangement of said primary ignition winding and thyristor beingconnected in parallel circuit relationship to said ignition capacitor.

4. An ignition device as claimed in claim 1, wherein said gating circuitincludes a set of contacts: capable of being open and closed insynchronization with the rotation of the engine, a gating capacitorcharged by said source upon the opening of said set of contacts, and aresistor connected to said gating capacitor to be traversed by acharging current for the latter to produce a voltage'applied as a gatingsignal to said thyristor.

1. An ignition device for use with an internal combustion engine,comprising, in combination:
 1. a source of direct current;
 2. invertermeans including a transformer comprising a saturable magnetic core, aninput winding, an output winding and a feedback winding, all saidwindings being inductively disposed around said magnetic core and atransistor connected to both said input winding and said feedbackwinding;
 3. said primary winding having an end terminal and anintermediate terminal presenting to said output winding a turn ratiohigher than does said end terminal;
 4. a first conductor connected tosaid end terminal of said primary transformer winding and capable ofbeing energized by said source;
 5. a second conductor connected to saidintermediate terminal of said primary transformer winding and capable ofbeing energized by said source;
 6. a transfer switch connected betweensaid source and said first and second conductors such that, the sameconnects said source to said second conductor upon starting the engineand to said first conductor after the engine has been started and whenit is in operation;
 7. a rectifier for rectifying the output of theoutput winding of said transformer and an ignition capacitor chargedwith the rectified output of the output winding of said transformer ofsaid inverter means;
 8. an ignition coil including a primary winding anda secondary winding inductively coupled to each other, said primarywinding having one end connected to said ignition capacitor;
 9. athyristor for controlling said ignition capacitor and operative in itsclosed state to permit said ignition capacitor to be discharged intosaid primary ignition coil winding to produce an ignition voltage acrosssaid secondary coil ignition winding, said thyristor having a controlterminal;
 10. a gating circuit controlling said thyristor and having aninput terminal, means operable in synchronism with the rotation of theengine to produce a gating signal and an output terminal connected withthe control terminal of said thyristor; anD
 11. a pair of semiconductordiodes having input and output terminals, means connecting the outputterminals of both of said diodes to the input terminal of said gatingcircuit, means connecting the input terminal of one of said diodes withsaid first conductor, and means connecting the input terminal of theother of said diodes with said second conductor.
 2. inverter meansincluding a transformer comprising a saturable magnetic core, an inputwinding, an output winding and a feedback winding, all said windingsbeing inductively disposed around said magnetic core and a transistorconnected to both said input winding and said feedback winding;
 2. Anignition device as claimed in claim 1, wherein said transformer of saidinverter means includes additionally another of said inverter meansincludes additionally another input winding and a separate feedbackwinding inductively disposed around said magnetic core, and whereinanother transistor is connected to both said another input winding andsaid separate feedback winding, said transistors being alternatelyturned on and off.
 3. An ignition device as claimed in claim 1, whereinsaid primary ignition winding is serially connected to said thyristor,the series arrangement of said primary ignition winding and thyristorbeing connected in parallel circuit relationship to said ignitioncapacitor.
 3. said primary winding having an end terminal and anintermediate terminal presenting to said output winding a turn ratiohigher than does said end terminal;
 4. a first conductor connected tosaid end terminal of said primary transformer winding and capable ofbeing energized by said source;
 4. An ignition device as claimed inclaim 1, wherein said gating circuit includes a set of contacts capableof being open and closed in synchronization with the rotation of theengine, a gating capacitor charged by said source upon the opening ofsaid set of contacts, and a resistor connected to said gating capacitorto be traversed by a charging current for the latter to produce avoltage applied as a gating signal to said thyristor.
 5. a secondconductor connected to said intermediate terminal of said primarytransformer winding and capable of being energized by said source;
 6. atransfer switch connected between said source and said first and secondconductors such that, the same connects said source to said secondconductor upon starting the engine and to said first conductor after theengine has been started and when it is in operation;
 7. a rectifier forrectifying the output of the output winding of said transformer and anignition capacitor charged with the rectified output of the outputwinding of said transformer of said inverter means;
 8. an ignition coilincluding a primary winding and a secondary winding inductively coupledto each other, said primary winding having one end connected to saidignition capacitor;
 9. a thyristor for controlling said ignitioncapacitor and operative in its closed state to permit said ignitioncapacitor to be discharged into said primary ignition coil winding toproduce an ignition voltage across said secondary coil ignition winding,said thyristor having a control terminal;
 10. a gating circuitcontrolling said thyristor and having an input terminal, means operablein synchronism with the rotation of the engine to produce a gatingsignal and an output terminal connected with the control terminal ofsaid thyristor; anD
 11. a pair of semiconductor diodes having input andoutput terminals, means connecting the output terminals of both of saiddiodes to the input terminal of said gating circuit, means connectingthe input terminal of one of said diodes with said first conductor, andmeans connecting the input terminal of the other of said diodes withsaid second conductor.